1. Field of the Invention
The present invention generally relates to electrical switch mechanisms, and more particularly to apparatus for controlling the operation of an electric switch and which is responsive to excessively high temperature conditions to discontinue the flow of electrical current through the switch.
2. Description of the Prior Art
Electrical switches are often used in environments susceptible to the hazards of fire, the electrical current flowing through a switch being itself a potential source for ignition of flammable materials in the vicinity of the switch. Accordingly, the prior art includes a variety of switch devices which can be included in an electrical circuit between a source of electrical power and electrical equipment powered by said source, the switch devices being capable of interrupting the supply of electrical power to the electrical equipment in the event of excessively high temperature conditions caused by fire or overheating of the electrical equipment. Sullivan, in U.S. Pat. No. 2,912,535, provides a temperature responsive electrical switch which is also responsive to vibration and shock. Stichling, in U.S. Pat. No. 3,915,236, provides a safety device associated with an electrical appliance and operative on subjection to a sufficient level of heat to discontinue the flow of electricity through the circuit in which the switch is disposed. Phillips et al, in U.S. Pat. No. 2,085,386, discloses a fusible element which, on melting due to excessive thermal conditions, causes a switch to open, thereby discontinuing the flow of electrical current through the switch. While the prior art has provided switch mechanisms capable of discontinuing the flow of electrical current through a circuit in which the switch is disposed on exposure to unusually high heat levels, the prior art has not provided an electrical switch mechanism normally operated by a manually-operated plunger whereby the plunger is rendered ineffective on melting of a fusible link disposed within the mechanism. On melting of the fusible link of the present invention, the switch mechanism cannot be further operated without replacement of the link. The present invention, therefore, provides a manually-operable electrical switch mechanism capable of discontinuing the flow of electrical current within a circuit to alleviate hazardous conditions which would occur on continuation of electrical current flow, the switch mechanism of the invention not being capable of accidental reactivation prior to termination of the unusual thermal conditions causative of melting of the fusible element within the present switch mechanism.